In the picture above, what do the “-S” and B for? The B (brake) slot is for supplementary braking as assisted by the engine, what we call “engine braking”. What happens when you let go of the accelerator in a manual car at a very low gear? That is engine braking at work, and it is more pronounced in lower gears than in higher ones. Engine braking supplements the wheel brakes, thus reducing the likelihood of overheating and suffering brake fade.

Source: Daily Nation January 23, 2018 18:55 UTC